Device and method for gas turbine unlocking

ABSTRACT

An aeroderivative gas turbine including an air intake plenum; a compressor with a compressor air intake in fluid communication with the air intake plenum; a combustor; a high pressure turbine; a power turbine. A forced air-stream generator is arranged in fluid communication with the air intake plenum. A shutter arrangement is provided in a combustion-air flow path, arranged and controlled to close the combustion-air flow path for pressurizing said air intake plenum by means of the forced air-stream generator to a pressure sufficient to cause pressurized air to flow through the aeroderivative air turbine.

FIELD OF THE INVENTION

The present disclosure relates generally to gas turbines, particularly,to aeroderivative gas turbines. More specifically, the presentdisclosure relates to devices and methods for unlocking a gas turbine,following the shut-down and rotor locking due to temperaturedifferentials inside the turbomachinery.

DESCRIPTION OF THE RELATED ART

Aeroderivative gas turbines are widely used as power sources formechanical drive applications, as well as in power generation forindustrial plants, pipelines, offshore platforms, LNG applications andthe like.

The gas turbine can be subject to shut-down, e.g. in emergencysituations, and re-started after a brief time period. When the rotor ofthe turbine is left motionless upon shut-down, thermal deformations mayoccur with the reduction or elimination of clearances between rotor andstator parts, hence leading to a rubbing between rotor and stator partsor a rising up to rotor locking phenomena. Thermal deformations arerelated to not uniform temperature fields, due to several factors.Cooling of the rotor when the turbine is motionless is non-uniform, theupper part of the rotor cools at a lower rate than the lower one, due tonatural convectional phenomena, thus generating rotor bending and bowingdeformations. Reduction of clearances between stator and rotor can alsoarise from temperature spreads related to the secondary flowdistribution during shut-down. The turbine cannot be restarted until therotor has reached the proper temperature field, as well as geometry.Under this respect, the most critical parts of the aeroderivative gasturbine are the blade tips in the compressor stages, where a limitedclearance is provided between the stator and the rotor.

For some types of gas turbine-emergency shut-down the cool-down processrequires significant amount of time, during which the turbine and thedriven load can therefore not be re-started. This can cause substantialeconomic loss and/or create technical or management problems.

It has been suggested to solve this problem by keeping the turbine rotorrevolving under a slow turning condition during the shut-down period,thus avoiding non-uniform cool-down of the rotor and preventing thelatter from locking. This is usually done by driving the turbine rotorinto rotation by means of the start-up electric motor. The start-upelectric motor requires a large amount of electric energy to be powered.For some particular plant emergency shut-down conditions, no AC currentis available, thus no start-up motor or any high energy consumptionutility may be used.

SUMMARY OF THE INVENTION

To reduce the downtime required to cool down the gas turbine followingshut-down and locking, a forced air-stream generator is provided whichgenerates a stream of forced cooling air at a pressure sufficient tocirculate the cooling air throughout the gas turbine when the latter isin a locked mode. The forced air stream reduces the time required tounlock the turbine rotor, so that the gas turbine can be re-startedafter a substantially shorter time interval than when no forced coolingair is provided.

U.S. Pat. No. 4,003,200 discloses a turbomachinery system wherein anauxiliary blower is connected to the air supply line. In this case,however, the blower is used to generate an air flow which is used tokeep the rotor of the turbomachinery in a slow-rolling condition. Thisprior art arrangement does not address the problem of unlocking a gasturbine after shut-down, however.

According to one embodiment, an aeroderivative gas turbine is provided,comprised of an air intake plenum, a compressor with a compressor airintake in fluid communication with the air intake plenum, a combustionchamber, a high pressure turbine, and a power turbine. A forcedair-stream generator is advantageously arranged in fluid communicationwith the air intake plenum. Moreover, a shutter arrangement is providedin a combustion-air flow path through which air entering the gas turbineflows. The shutter arrangement is arranged and controlled to close thecombustion-air flow path so that the air intake plenum is pressurized bymeans of the forced air-stream generator up to a pressure sufficient tocause pressurized air to flow through said aeroderivative turbine, whilethe latter is non-rotating, e.g. following locking after shut-down. Theforced cooling air stream generated by the forced air-stream generatorremoves heat from the turbomachinery such that the effect of the thermaldifferential expansion which causes the locking of the rotor will beneutralized in a time shorter than with the absence of forced cooling.

In some embodiments, a silencer arrangement is provided in thecombustion-air flow path. In this case, the shutter arrangement can bedisposed downstream of the silencer arrangement with respect to an airstream in said combustion-air flow path.

The silencer arrangement may comprise a plurality of parallel arrangedsilencer panels, defining air passageways there between, each airpassageway having an air outlet aperture. A pivoting shutter can bearranged at each air outlet aperture, to selectively open and close theair passageway. The pivoting shutters can be operated each by anindependent actuator. In some embodiments, however, the shutters areconnected to one another such as to be simultaneously controlled by acommon opening and closing actuator.

Each pivoting shutter may be pivoting around a respective pivotingshaft. The pivoting shaft may be positioned so as to extend parallel toa respective silencer panel and downstream a trailing edge of saidsilencer panel. The trailing edge is the most downstream edge of thepanel referring to the air flow direction.

In some embodiments, an inclined plate is arranged parallel to eachpivoting shaft and extends in an air flow direction downstream eachsilencer panel. When the shutter is in the opened position, the inclinedplate and the shutter can take a mutual position so that they convergeto one another in the air flow direction and can be designed andarranged to form a low pressure drop profile extending downstream therespective silencer panel, whose cross section diminishes in the airflow direction.

According to some embodiments, each silencer panel has planar surfaces,opposing planar surfaces of each pair of adjacent silencer panelsdefining a respective air passageway. Each air passage can have asubstantially rectangular cross section with a first dimension parallelto the planar surfaces of the silencer panels and a second dimensionorthogonal to said planar surfaces. The first dimension is larger thanthe second dimension, e.g. ten times larger, i.e. the air passagewayshave a rectangular cross section with a long side and a short side, theshort side being e.g. 10 times shorter than the long side, or smaller.

To achieve a better closure of the air intake plenum, and therefore amore efficient forced cooling of the gas turbine, at least some, and, inan embodiment, each, air outlet aperture is at least partly surroundedby a sealing gasket co-acting with the respective shutter. In someembodiments, each air outlet aperture is entirely surrounded by asealing gasket. The sealing gasket may have a self-sealing shape. Aself-sealing shape is one which increases the sealing effect when theair pressure in the air intake plenum increases.

For example, the sealing gasket may comprise a gasket body and a sealinglip projecting from the gasket body. The sealing lip may be arranged anddesigned to co-act with the respective shutter when the shutter is in aclosed position, pressure in the air intake plenum forcing the sealinglip against the shutter.

Each air outlet aperture may be at least partly surrounded by a gasketretention profile, to anchor the sealing gasket and retain it inposition.

In some embodiments an end-stop may be provided for each air outletopening, said end-stop defining a closing position of the respectiveshutter, so that the pressure inside the air intake plenum will notsqueeze the sealing gasket. This prevents mechanical damage to thesealing gasket.

In some embodiments the forced air-stream generator is designed andarranged to prevent air flow there through when said forced air-streamgenerator is inoperative. This could be advantageously achieved e.g. byusing a positive displacement compressor, e.g. a rotary compressor, suchas a Roots compressor, or a screw compressor or the like.

According to a further aspect, the present disclosure concerns a methodfor unlocking a rotor in an aeroderivative gas turbine followingshut-down of said turbine, comprising the following steps: providing anair intake plenum in fluid communication with a combustion-air flowpath, a compressor air intake of the aeroderivative gas turbine and aforced air-stream generator, providing a shutter arrangement, arrangedand controlled to close the combustion-air flow path, cooling said rotorof the aeroderivative gas turbine when the rotor is locked followingshut down, by closing the shutter arrangement and generating anoverpressure in the air intake plenum by means of the forced air-streamgenerator, the overpressure being sufficient to force pressurized airthrough the locked rotor of the aeroderivative gas turbine.

Features and embodiments are disclosed here below and are further setforth in the appended claims, which form an integral part of the presentdescription. The above brief description sets forth features of thevarious embodiments of the present invention in order that the detaileddescription that follows may be better understood and in order that thepresent contributions to the art may be better appreciated. There are,of course, other features of the invention that will be describedhereinafter and which will be set forth in the appended claims. In thisrespect, before explaining several embodiments of the invention indetails, it is understood that the various embodiments of the inventionare not limited in their application to the details of the constructionand to the arrangements of the components set forth in the followingdescription or illustrated in the drawings. The invention is capable ofother embodiments and of being practiced and carried out in variousways. Also, it is to be understood that the phraseology and terminologyemployed herein are for the purpose of description and should not beregarded as limiting.

As such, those skilled in the art will appreciate that the conception,upon which the disclosure is based, may readily be utilized as a basisfor designing other structures, methods, and/or systems for carrying outthe several purposes of the present invention. It is important,therefore, that the claims be regarded as including such equivalentconstructions insofar as they do not depart from the spirit and scope ofthe present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosed embodiments of theinvention and many of the attendant advantages thereof will be readilyobtained as the same becomes better understood by reference to thefollowing detailed description when considered in connection with theaccompanying drawings, wherein:

FIGS. 1A and 1B illustrate a schematic side view of an aeroderivativegas turbine package, comprising a forced-air system for turbine rotorunlocking, in two different operating conditions;

FIG. 1C illustrates a schematic longitudinal section of an exemplaryembodiment of an aeroderivative gas turbine;

FIG. 2 illustrates an isometric view of a shutter arrangement of theforced-air system in one embodiment;

FIG. 3 illustrates a plan view of the shutter arrangement of FIG. 2;

FIG. 4 illustrates a cross-section according to line IV-IV in FIG. 3;

FIG. 4A illustrates an enlargement of detail A in FIG. 4 with theshutter arrangement in the closed position;

FIG. 5 illustrates a side view according to line V-V in FIG. 3;

FIG. 6 illustrates a cross-section according to line VI-VI in FIG. 5;

FIG. 7 illustrates a vertical cross section of the upper portion of anair intake plenum in a different embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The following detailed description of the exemplary embodiments refersto the accompanying drawings. The same reference numbers in differentdrawings identify the same or similar elements. Additionally, thedrawings are not necessarily drawn to scale. Also, the followingdetailed description does not limit the invention. Instead, the scope ofthe invention is defined by the appended claims.

Reference throughout the specification to “one embodiment” or “anembodiment” or “some embodiments” means that the particular feature,structure or characteristic described in connection with an embodimentis included in at least one embodiment of the subject matter disclosed.Thus, the appearance of the phrase “in one embodiment” or “in anembodiment” or “in some embodiments” in various places throughout thespecification is not necessarily referring to the same embodiment(s).Further, the particular features, structures or characteristics may becombined in any suitable manner in one or more embodiments.

FIGS. 1A and 1B schematically illustrate a side view and a partialcross-section of an aeroderivative gas turbine installation. In FIG. 1Athe gas turbine is in operation and in FIG. 1B the gas turbine isinoperative, while the unlocking arrangement is running.

The installation is labelled 100 as a whole. The installation comprisesa package 101 and an aeroderivative gas turbine 102 arranged therein.Upstream of the aeroderivative gas turbine 102 an air intake plenum 103is provided. The air intake plenum 103 is in fluid communication with acombustion-air flow path 105 extending above the air intake plenum 103.The inlet side of the combustion-air flow path 105 is provided withfilters 107. Inside the combustion-air flow path 105 a silencerarrangement 109 is provided to reduce the noise generated by air intake.

As will be described in greater detail below with reference to FIG. 1A,the aeroderivative gas turbine 102 comprises a plurality of sections,including a compressor section, a combustor, a high pressure turbine anda power turbine. The aeroderivative gas turbine 102 further comprises anouter casing 102C enclosing the compressor and the turbines as well asthe combustor. The casing 102C of the aeroderivative gas turbine 102 issurrounded by the package 101 which defines an inner volume 101A.Cooling air is circulated around the casing 102C and discharged througha discharging duct 115. Exhaust combustion gases discharged from thepower turbine exit the package through an exhauster 117. In thediagrammatic representation of FIGS. 1A and 1B a driven shaft 119 isprovided on the hot side of the aeroderivative gas turbine 102, to drivea generic load 121, for example an electric generator, a compressor or acompressor train of a natural gas liquefaction line, or any othersuitable load.

In some embodiments, on the side of the air intake plenum 103 opposingthe aeroderivative gas turbine 102, a compartment 106 is arranged whichis in fluid communication with an air intake duct 113 and with theinterior 101A of the turbine package 101. An air fan 110 can be arrangedin the air intake duct 113. Alternatively, an air fan 112 may bearranged in the discharging duct 115. A combination of more fans is notexcluded. The air fan(s) 110 and/or 112 generate a cooling air streamwhich enters the interior 101A of the gas turbine package 101 by flowingthrough the air intake duct 113 and the compartment 106 and around theair intake plenum 103 to cool the gas turbine casing 102C.

According to the embodiment illustrated in FIGS. 1A and 1B, a forcedair-stream generator 111 is arranged in the compartment 106. In someembodiments the forced air-stream generator 111 comprises a positivedisplacement compressor, such as a rotary volumetric compressor.Suitable rotary compressors are rotary lobe compressors, such as Rootscompressors, screw compressors or vane compressors. In more generalterms, the forced air-stream generator 111 is comprised of a means toprevent air from flowing through the forced air-stream generator whenthe latter is not operating. If a positive displacement compressor isused, such as a Roots compressor, air flow through the compressor isprevented when the compressor is inoperable, without the need for anadditional check valve arrangement, or the like. This makes thearrangement simpler and less expensive.

The forced air-stream generator 111 can be driven by a mover, such as anelectric motor 114, for example. The inlet side of the forced air-streamgenerator 111 is shown in 111A and the outlet side is shown in 111B. Theinlet side 111A is in fluid communication with the compartment 106,while the outlet side 111B is in fluid communication with the air intakeplenum 103, so that when the forced air-stream generator is operating,air is sucked through the air intake duct 113 and flows forcedly throughthe air intake plenum 103 for the purposes which will be clarifiedafter.

Referring now to FIG. 1C, in some embodiments the aeroderivative gasturbine 102 comprises a compressor section 9, including a compressorfront frame or bell mouth 11, forming a compressor air-intake, a casing13 and a rotor 14 supported in a rotating manner by a shaft 16 andarranged in the casing 13. Rotary blades on the rotor 14 and stationaryblades on the casing 13 cause air to be sucked through the bell mouth11, compressed and fed to an outlet 15 of the compressor section 9.Outlet 15 is in fluid communication with a combustor 17. Compressed airexiting the compressor section 9 is fed into combustor 17, together witha gaseous or liquid fuel.

Combustor 17 is in fluid communication with a high pressure turbine 19.The high pressure turbine 19 is driven into rotation by the combustiongases flowing there through and provides power to drive the compressorsection 9. Only part of the power available is used by the high pressureturbine 19 to drive the compressor. Hot gases exiting the high pressureturbine 19 are still pressurized and will be used in a downstreamsection of the aeroderivative gas turbine to generate mechanical power.The combination of compressor section 9, combustor 17 and high pressureturbine 19 is usually named gas generator and is designated 20 as awhole in the drawings.

In the embodiment illustrated in the drawings, the rotor 14 of thecompressor section 9 and the rotor of the high pressure turbine 19 aresupported by a common shaft 16 and jointly form a gas generator rotor.

The gas generated by the gas generator 20 and exiting the high pressureturbine 19 flows through a power turbine section downstream, wherein theenergy contained in the gas is partly transformed into mechanicalenergy.

In the exemplary embodiment shown in the drawings, the power turbinesection comprises a low pressure power turbine 21, which comprises astator 21S and a rotor 21R. In the embodiment illustrated in thedrawings, rotor 21R of the power turbine 21 is supported on andtorsionally connected to a turbine shaft 22, which is mechanicallyseparated from shaft 16 of the gas generator.

The power turbine 21 can include a variable number of expansion stages.The exemplary embodiment illustrated in FIG. 1A includes a low speed,six-stages power turbine. Other embodiments can include a high-speedpower turbine, e.g. a high-speed, two-stages power turbine. Exhaustgases exiting the power turbine in 23 can be used for co-generationpurposes, or simply discharged into the atmosphere.

The aeroderivative gas turbine illustrated in FIG. 1C is only anexample. Various and different commercially available aeroderivative gasturbines can be used in this application. The overall structure andlayout, including the number of compressors, the number of turbines, thenumber of shafts and the number of compression and expansion stages, mayvary from one aeroderivative gas turbine to another. Suitableaeroderivative gas turbines are LM2500 Plus G4 HSPT or LM2500 Plus6-Stage gas turbines: Both are commercially available from GE Aviation;Evendale, Ohio; USA. Other suitable aeroderivative gas turbines are thePGT25+ aeroderivative gas turbine; commercially available from GE Oiland Gas; Florence, Italy; or the Dresser-Rand Vectra® 40G4aeroderivative gas turbine, commercially available from Dresser-RandCompany; Houston, Tex.; USA. In other embodiments, the aeroderivativegas turbine could be a PGT16, a PGT 20, or a PGT25; all commerciallyavailable from GE Oil and Gas; Florence, Italy. Also suitable is anLM6000 aeroderivative gas turbine; commercially available from GEAviation; Evendale, Ohio; USA.

In some embodiments, the shaft of the aeroderivative gas turbine candrive the load 121 directly, i.e. with a direct mechanical connection,so that the load 121 rotates at substantially the same speed as thepower turbine of the aeroderivative gas turbine 102. In otherembodiments, a gearbox can be arranged between the shaft of the powerturbine and the shaft of the load 121. The particular arrangementdepends on design considerations, based on the kind of power turbineused (high speed or low speed) and/or on the rotary speed of load 121.

In the combustion-air flow path 105, downstream of the silencerarrangement 109, a shutter arrangement 123 is provided: The operationand structure whereof will be described in greater detail below. As willbe described with greater detail below, the shutter arrangement 123 isclosed and the forced air-stream generator 111 is started whenever,following shut-down of the aeroderivative gas turbine, the rotor of theaeroderivative gas turbine, and specifically the rotor of the gasgenerator, is locked and requires to be cooled down and unlocked toallow the aeroderivative gas turbine to restart.

Referring specifically to FIGS. 2 through 6, a first embodiment of theshutter arrangement 123 will now be described.

In advantageous embodiments, the shutter arrangement 123 is positionedunderneath the silencer arrangement 109, as shown in FIG. 1, i.e.downstream of said silencer arrangement 109, with respect to theair-flow direction. The silencer arrangement 109 may include a pluralityof parallel silencer panels 131. The silencer panels are, in anembodiment, flat or planar. Between each pair of adjacent silencerpanels 131, a respective air passageway is formed. As will be clarifiedin the following description, the shutter arrangement 123 comprises apivoting shutter for each air passage way, to provide an efficientclosure of the combustion-air flow path 105, downstream of the silencerarrangement 109.

In the embodiment illustrated in FIGS. 2 through 6, the shutterarrangement 123 comprises a frame 135. In an embodiment, the frame 135is comprised of side profiles 137, 138, 139 and 140, connected togetherto form a rectangular or square frame 135. In some embodiments, theouter dimension of the frame 135 matches the cross section of thecombustion-air flow path 105.

In the exemplary embodiment illustrated in the drawings, a plurality ofbeams 143 is arranged inside of the frame 135. Each beam 143 spansacross the width of the frame 135 from profile 137 to profile 139. Thebeams 143 are spaced one from the other to define an air passageway 145between each pair of adjacent beams 143.

As can be appreciated from the schematic representation of FIG. 4, eachbeam 143 is arranged underneath the lower edge of one of the silencerpanels 131, which form the silencer arrangement 109. In someembodiments, the beams 143 have a square or rectangular cross-section.However, it should be understood that different cross-sections may beused.

The air passageways 145, defined between the adjacent and parallel beams143, form an extension of corresponding passageways 147 defined betweenthe corresponding parallel silencer panels 131. In this way, in the areaof the silencer arrangement 109 and of the shutter arrangement 123, theinterior of the combustion-air flow path 105 is divided into a pluralityof side by side arranged air passageways 145, 147. Each passageway has arectangular cross-section. More specifically, the cross-section of eachair passageway 145, 147 has a first dimension D1 and a second dimensionD2. The first dimension D1 corresponds to the width of the silencerpanels 131 and to the length of the beams 143, while the seconddimension D2 corresponds to the distance between adjacent beams 143. Insome embodiments, the dimension D1 is several times larger than thedimension D2. In some embodiments, the dimension D1 is at least tentimes greater than D2 or greater.

Each air passageway 145, 147 has an air outlet aperture formed by thetwo respective parallel beams 143 and the two opposing profiles 137 and139. The air inlet aperture, labelled 145A in FIGS. 4 and 4A, issurrounded by a sealing gasket, co-acting with a pivoting shutter, aswill be further described below.

In some embodiments, from the lower sidewall of each beam 143 aninclined plate 149 extends towards the air intake plenum 103. Eachinclined plate 149 develops along the entire length of the respectivebeam 143 and is arranged such as to converge in the downstream directiontowards a vertical median plane of the corresponding beam 143, as wellas the corresponding silencer panel 131.

In some embodiments, underneath each beam 143, i.e. downstream of eachbeam 143, with respect to the air flowing through the combustion-airflow path 105 towards the air intake plenum 103, a shutter 151 ispivotally supported by a corresponding pivoting shaft 153. Each pivotingshaft 153 (see in particular FIG. 6) is supported at both ends bysupporting bearings 155 and 157. In the exemplary embodiment shown inFIG. 6, the bearing 155 of each pivoting shaft 153 is supported by theprofile 137 and each bearing 157 is supported by the opposing profile139. Each pivoting shaft 153 may therefore pivot around its axis A-A.

Each pivoting shaft 153 is provided with a lever 154 (see in particularFIG. 5). The levers 154 of pivoting shafts 153 are all connected, one tothe other, by rods 159. The rods 159 form a sort of composite shaftextending from the first to the last of the various levers 154, so thatby means of a single actuator (for example a cylinder-piston actuatorschematically shown at 160 in FIG. 5) all the pivoting shafts 153 may bepivoted simultaneously around their own axis A-A, to obtain thesimultaneous opening and closing of the shutters 151. The pivotingmovement is a reciprocating rotary movement of around 90°.

In some embodiments, each shutter 151 is comprised of a flat panel whichis torsionally constrained to the respective pivoting shaft 153, so thatthe reciprocating rotation of each pivoting shaft 153 causes acorresponding reciprocating rotation according to double arrow f151 ofthe respective shutter 151 (FIG. 4A).

By controlling the pivoting movement around the axis A-A of therespective pivoting shaft 153, each shutter 151 may be moved from anopen position (FIG. 4) to a closed position (FIG. 4A) and vice-versa.

In the open position (FIG. 4) each shutter 151 is positioned underneaththe respective beam 153. In some embodiments, each shutter 151 and thecorresponding inclined plate 149 form a sort of trailing edge extendingbeyond the silencer panel 131 and the respective beam 143 in thedirection of air flow towards the air intake plenum 103, when theshutters 151 are in the open position. This arrangement significantlyreduces both the air flow pressure drop and noise.

By simultaneously rotating all the pivoting shafts 153 around the axesA-A thereof by means of the actuator 160, all of the shutters 151 aresimultaneously brought into the closed position shown in FIG. 4A. Inthis position, each shutter 151 entirely closes the respective air inletaperture 145A.

In some embodiments, each air inlet aperture 145A is surrounded by asealing gasket 163. The air inlet aperture 145A has a narrow rectangularcross-section with dimensions D1-D2. The sealing gasket 163 is thereforecorrespondingly formed by rectilinear gasket portions extending aroundthe rectilinear edges of the air inlet aperture 145A. The sealing gasket163 can be formed by portions of an extruded profile, cut at 45° andglued or soldered together to take the shape of a narrow and elongatedrectangular sealing gasket.

In some embodiments, the closed position of each shutter 151 is definedby an end-stop 150, which prevents the shutter from excessivelysqueezing or pinching the sealing gasket 163 when the shutter is in theclosed position (FIG. 4A).

In some embodiments, the sealing gasket 153 is retained in its positionby restraining it into a channelled profile 165, formed by a metalsection of suitable cross section, as particularly shown in FIG. 4A. Thechannelled profile 165 extends around the entire air inlet aperture 145Aand holds the sealing gasket 163 in place.

For a more efficient sealing effect, in some embodiments, the sealinggasket 163 comprises a gasket body 163B which is forcefully retained inthe corresponding channelled profile 165, and further comprises a firstlip 163X and a second lip 163Y. The two lips 163X and 163Y diverge,forming a wedged shaped space 163S. In the closed position (FIG. 4A) theshutter 151 is pressed against the lower lip 163Y. The sealing action ofthe lip 163Y against the upper surface of the shutter 151 is increasedby the air pressure in the air intake plenum 103, due to the flexibilityof the lip 163Y and the wedged shaped space 163S between the two lips163X and 163Y. In this manner, efficient sealing is achieved even byapplying a small torque to the pivoting shafts 153.

If the rotor of the gas generator of the aeroderivative gas turbine 102becomes locked, following the turbine shut-down, e.g. due to rubbing ofthe compressor blades against the inside of the compressor casing, inorder to reduce the downtime required to cool-down the rotor and unlockthe gas turbine, the shutter arrangement 123 is closed and the forcedair-stream generator 111 is started. Air is sucked through the airintake duct 113 and pressurized by the forced air-stream generator 111in the air intake plenum 103 to such a value that air flows through thelocked rotor of the aeroderivative gas turbine 102. In some embodimentsan air pressure between 0.05 and 0.3 Bar and, in an embodiment, between0.1 and 0.15 Bar above ambient pressure is desired within the air intakeplenum 103. Under these pressure conditions an air flow through theaeroderivative gas turbine 102 is generated. The air flow cools the gasgenerator rotor, the turbine rotor and the casing down and is maintaineduntil the rotor is unlocked. The cooling down and unlocking is achievedin a reduced time allowing the quick restarting of the aeroderivativegas turbine 102.

The special sealing gasket arrangement described above is particularlyefficient in closing the combustion-air flow path 105 and avoidingbackflow, from the air intake plenum 103 towards the environment, whenthe forced air-stream generator 111 is operative.

FIG. 7 schematically illustrates a cross section along a vertical planeof an air intake plenum 103 provided with a different shutterarrangement. In this embodiment the shutter arrangement, again labelled123 as a whole, comprises a single door or hatch 170 hinged at 171 to aside wall of the air intake plenum 103, such as to pivot around ahorizontal axis, to selectively open or close the combustion-air flowpath 105. A cylinder-piston actuator 173 controls the pivoting movementaccording to the double arrow f170 of the door or hatch 170, to move itfrom an open position (shown in solid lines in FIG. 7) to a closedposition (shown in dotted lines in FIG. 7), in which the door 170 closesthe combustion-air flow path 105 downstream of the silencer arrangement109.

The operation of the gas turbine arrangement described so far, is thefollowing. When the gas turbine is running (FIG. 1A), air flowingthrough the combustion-air flow path 105, the silencer arrangement 109and the shutter arrangement 123 (arrows A in FIG. 1A) enters the airintake plenum 103 and the gas turbine 102. Combustion gases generated bythe gas generator are expanded in the power turbine and dischargedthroughout the exhauster 117. Cooling air (arrow C) flows through theair intake duct 113, the interior 101A of the gas turbine package 101and escapes trough the discharge duct 115. Air is prevented from flowingfrom the air intake plenum 103 through the forced air-stream generator111 in the compartment 106 by the very nature of the device used, namelye.g. a positive displacement compressor.

If the gas turbine is shut down, already after a short time the gasgenerator rotor becomes locked due to rubbing. The gas turbine must beallowed to cool down until a sufficiently uniform temperaturedistribution (temperature field) is achieved, so that the gas generatorrotor becomes free again to rotate.

To reduce the downtime required to restart the gas turbine, the forcedair-stream generator 111 is used to generate a forced cooling air streamthrough the gas turbine. In order for the forced air-stream generator111 to operate properly, the shutter arrangement 123 is closed toprevent air from the forced air-stream generator 111 from escapingthrough the combustion-air flow path 105.

The forced air-stream generator 111 is started by activating the motor114. Air is thus sucked through the air intake duct 113 and delivered ata sufficient overpressure to the air intake plenum 103 and is caused toforcedly flow through the gas turbine and to exit from the exhauster117, see arrows D in FIG. 1B

The cooling air forcedly flows through the stationary (non-rotating)aeroderivative gas turbine 102, cooling the rotor and the casing of theaeroderivative gas turbine 102 and removing heat by forced convection.The rotor becomes unlocked in a much shorter time than required, if noforced cooling is provided. The time required to unlock the rotor canvary depending on the turbine design, or other factors. Tests performedon a PGT25+ gas turbine resulted in a total unlocking time of around 40minutes. In general, the cooling time required using a forced air systemas disclosed above ranges typically between 30 and 90 minutes. It shouldbe understood that these numerical values are given by way of exampleand should not be construed as limiting the scope of the disclosure,since several parameters can influence the actual total time required toachieve the unlocking of the rotor.

While the disclosed embodiments of the subject matter described hereinhave been shown in the drawings and fully described above withparticularity and detail in connection with several exemplaryembodiments, it will be apparent to those of ordinary skill in the artthat many modifications, changes, and omissions are possible withoutmaterially departing from the novel teachings, the principles andconcepts set forth herein, and advantages of the subject matter recitedin the appended claims. Hence, the proper scope of the disclosedinnovations should be determined only by the broadest interpretation ofthe appended claims so as to encompass all such modifications, changes,and omissions. In addition, the order or sequence of any process ormethod steps may be varied or re-sequenced according to alternativeembodiments.

What is claimed is:
 1. An aeroderivative gas turbine comprising: an airintake plenum; a compressor with a compressor air intake in fluidcommunication with the air intake plenum; a combustor; a high pressureturbine; a power turbine; a forced air-stream generator arranged influid communication with the air intake plenum; and a shutterarrangement provided in a combustion-air flow path through which airenters the air intake plenum, the shutter arrangement being arranged andcontrolled to close the combustion-air flow path to pressurize the airintake plenum by the forced air-stream generator, up to a pressuresufficient to force pressurized air through the aeroderivative gasturbine.
 2. The aeroderivative gas turbine according to claim 1, furthercomprising a silencer arrangement arranged in the combustion-air flowpath, wherein the shutter arrangement is disposed downstream of thesilencer arrangement with respect to an air stream in the combustion-airflow path.
 3. The aeroderivative gas turbine according to claim 1,wherein: the silencer arrangement comprises a plurality of parallelarranged silencer panels, an air passageway is defined between each pairof adjacent silencer panels, each air passageway having an air outletaperture, and a shutter is movably arranged at each air outlet aperture,to selectively open and close the air passageway.
 4. The aeroderivativegas turbine according to claim 3, wherein the shutters are pivotingshutters arranged to reciprocatingly pivoting around respective axes toselectively open and close the air passageways.
 5. The aeroderivativegas turbine according to claim 3, wherein the shutters aresimultaneously controlled by an opening and closing actuator.
 6. Theaeroderivative gas turbine according to claim 4, wherein each pivotingshutter is arranged to pivot around a respective pivoting shaftextending parallel to a respective silencer panel and downstream atrailing edge of the silencer panel.
 7. The aeroderivative gas turbineaccording to claim 6, wherein an inclined plate is arranged parallel toeach pivoting shaft and extending in an air flow direction downstream ofeach silencer panel, the inclined plate and the shutter converging toone another in the air flow direction and being designed and arranged toform a trailing profile extending downstream of the respective silencerpanel.
 8. The aeroderivative gas turbine according to claim 3, whereineach the silencer panel has planar surfaces, opposing planar surfaces ofeach pair of adjacent silencer panels defining a respective airpassageway having a substantially rectangular cross section with a firstdimension parallel to the planar surfaces and a second dimensionorthogonal to the planar surfaces, the first dimension being larger thanthe second dimension.
 9. The aeroderivative gas turbine according toclaim 8, wherein the first dimension is at least ten times the seconddimension.
 10. The aeroderivative gas turbine according to claim 4,further comprising a beam arranged downstream of each silencer panelwith respect to the air flow in the combustion-air flow path, andwherein each shutter is pivoted downstream the beam.
 11. Theaeroderivative gas turbine according to claim 7, wherein each inclinedplate is supported by the respective beam and extends parallel thereto.12. The aeroderivative gas turbine according to claim 3, wherein eachair outlet aperture is at least partly surrounded by a sealing gasketco-acting with the respective shutter.
 13. The aeroderivative gasturbine according to claim 12, wherein each air outlet aperture isentirely surrounded by the sealing gasket.
 14. The aeroderivative gasturbine according to claim 12, wherein the sealing gasket has aself-sealing shape, so the sealing action of the sealing gasket isincreased by air pressure in the air intake plenum.
 15. Theaeroderivative gas turbine according to claim 12, wherein the sealinggasket comprises a gasket body and a sealing lip projecting from thegasket body, the sealing lip co-acting with the respective shutter whenthe shutter is in a closed position, pressure in the air intake plenumpressing the sealing lip against the shutter.
 16. The aeroderivative gasturbine according to claim 12, wherein the air outlet aperture is atleast partly surrounded by a gasket retention profile, the sealinggasket being anchored in the gasket retention profile.
 17. Theaeroderivative gas turbine according to claim 12, wherein an end stop isprovided for each air outlet opening, the end stop defining a closingposition of the respective shutter.
 18. The aeroderivative gas turbineaccording to claim 1, wherein the forced air-stream generator and thecompressor air intake are arranged facing each other in the air intakeplenum.
 19. The aeroderivative gas turbine according to claim 18,wherein the forced air-stream generator is arranged inside a gas turbinecompartment below a ventilation air entrance.
 20. The aeroderivative gasturbine according to claim 1, wherein the forced air-stream generator isconfigured to prevent air flow there through when the forced air-streamgenerator is inoperative.
 21. The aeroderivative gas turbine accordingto claim 20, wherein the forced air-stream generator comprises apositive displacement compressor.
 22. The aeroderivative gas turbineaccording to claim 21, wherein the forced air-stream generator comprisesa rotary compressor.
 23. A method for unlocking a rotor in anaeroderivative gas turbine following shut-down of the turbine, themethod comprising: providing an air intake plenum in fluid communicationwith a combustion-air flow path, a compressor air intake of theaeroderivative gas turbine and a forced air-stream generator; providinga shutter arrangement, arranged and controlled to close thecombustion-air flow path; and cooling the rotor of the aeroderivativegas turbine when the rotor is locked following shut down, by closing theshutter arrangement and generating an overpressure in the air intakeplenum by means of the forced air-stream generator, the overpressurebeing sufficient to force pressurized air through the locked rotor ofthe aeroderivative gas turbine.
 24. The method according to claim 23,wherein the overpressure ranges between 0.05 and 0.3 Bar above ambientpressure.
 25. The method according to claim 23, wherein the overpressureranges between 0.1 and 0.15 Bar above ambient pressure.